Nature of Luminescence Transitions in ZnS Crvstals

With the purpose to elucidate the nature of luminescence transitions in ZnS crystals, emission spectra from typical luminescence centers, “Green-Cu”, “Blue-Cu”, Self-Activated, “Red-Cu”, and “Red-Cu, In” centers, were measured at various temperatures. The results show that these luminescences can be divided into two growps, A and B, the former including “G-Cu” and “B-Cu”, while the latter SA, “R-Cu” and “R-Cu, In”. In B group, emission peaks shift towards higher energies with increase in temperature from 4°K accompanied by the remarkable increase of half-widths, while in A group emission peaks shift towards lower energies, half-widths increasing only slightly. These characteristics in B group were accounted for from the theoretical viewpoint based on the configurational coordinate model, indicating that the transition responsible for the luminescences takes place between two localized levels. As for A group it may be concluded that the transition is that of free electron or hole to localized level. Taking the Other luminescence properties into consideration, the types of the transitions as well as the nature of the relevant levels were discussed.